[teiid-issues] [JBoss JIRA] (TEIID-2359) BufferManager reserved thread local can keep buffermanager references alive

[Steven Hawkins (JIRA)]

    [ https://issues.jboss.org/browse/TEIID-2359?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12750605#comment-12750605 ] 

Steven Hawkins commented on TEIID-2359:
---------------------------------------

I need to correct my thoughts above.  The reserved by thread ThreadLocal will not keep a BufferManagerImpl reference alive as the ThreadLocal will be weakly held key - the value is just an Integer.

There is a related issue however with the BlockByteBuffer ThreadLocal.  There the value will hold a hard reference to the memory buffer and thus may keep the buffer reference around as long as the Thread is alive (or until the Java internal ThreadLocalMap is compacted and tested for gc'ed keys).

I should also add this is only an issue when using local connections that use the calling thread - otherwise all of the relevant threads will be stopped with the DQP pool is shutdown/dereferenced.
                
> BufferManager reserved thread local can keep buffermanager references alive
> ---------------------------------------------------------------------------
>
>                 Key: TEIID-2359
>                 URL: https://issues.jboss.org/browse/TEIID-2359
>             Project: Teiid
>          Issue Type: Feature Request
>          Components: Query Engine
>    Affects Versions: 8.0
>            Reporter: Steven Hawkins
>            Assignee: Steven Hawkins
>
> The most common implementation of ThreadLocal holds does not garbarge collect ThreadLocal values when the ThreadLocal goes out of scope - only when the Thread stops.  Thus the BufferManager reserved threadlocal being a non-static inner class is inadvertently keeping a reference alive. 
> Marked as starting with Teiid 8.0 as selective Teiid restarts (which is how multiple instances are introduced) are not performed in the 7.x series.

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